I can't figure out why that keel wood was there, but it was. Removing the rotten piece is proper but in my mind you need to replace the possible structural properties with something, like a bunch of scrap composite board, or mixture of chopped glass and epoxy. Could also add some other filler like cabosil with maybe some wood filler. So after you grind up all the glass along the keel gap, then fill it and after it sets and you've ground it properly, cover it with a couple layers of 1708.